The flagellum of Campy/obaeter jejuni is a major virulence determinant, dependent on
about 40 flagellar genes that are co-ordinately expressed. However, the existence of a
flagellar regulon in C. jejuni and the genes that may control it are so far undefined.
To elucidate this, three putative global regulatory gene homologues, rpoN, fliA and
flgR encoding the alternative sigma factors, 0'54, 0'28 and the 0'54 -associated transcriptional
activator FlgR respectively, were selected. The genes were cloned and mutated by inverse
PCR mutagenesis. Kanamycin resistant mutants were constructed by allelic replacement in
two C. jejuni strains, NCTC 11168 and NCTC 11828. Electron microscopic studies showed
that the rpoN and flgR mutants were nonflagellate; the fliA mutant had truncated flagella.
Immunoblotting confirmed lack of flagellin expression in the rpoN and flgR mutants and
partial flagellin expression in the fliA mutant. Thus neither the flaB gene with a 0'54 promoter
encoding the minor flagellin, nor the flaA gene with a 0'28 promoter encoding the major
flagellin are expressed in the rpoN andflgR mutants. These observations confirm the roles of
rpoN,flgR andfliA gene homologues in flagellar expression in C.jejuni.
Promoter analysis of all the flagellar genes in C. jejuni shows that rpoN and flgR are
essential regulatory genes in the putative flagellar regulon of C. jejuni. Microarray
hybridisations and analyses reveal that mutation of the rpoN and/or flgR genes affects
regulation of expression of several flagellar genes. These analyses shed light on the distinct
difference in flagellar regulon between enteric bacteria and C. jejuni and outline the flagellar
regulon of the latter.
Studies were also carried out with two putative flagellar regulatory genes, Inr and
regX3. However, mutations in these genes did not affect the nature of the flagella.